Increasing demand for higher capacity, lower cost data storage has pushed the technologies of silicon-based semiconductor memory chips and magnetic hard disk drives (HDDs) towards their theoretical limits. HDDs have dominated the data storage market, and have increased storage densities at a rate of 60–100% per year. However, the area density that may be achieved by current magnetic recording technology will eventually reach a limit, imposed by a known superparamagnetic effect believed to be in the order of 250 Gbit/in2 for longitudinal recording.
Atomic force and scanning tunneling microscopes use nanometer sized tips for imaging and investigating the structure of materials down to atomic levels. These devices have led to the development of ultrahigh density storage devices that utilize micro electro mechanical system (MEMS) based arrays of tips that write, read and erase data on a recording medium using magnetic, optical, electric and/or thermal processes. For example, these tips may utilize a magnetic or physical method of marking or otherwise changing the recording medium to write or erase a data element. Retrieval of the data element at a later time is accomplished using the same or similar tips to detect the mark or change in the recording medium.
As appreciated, a thermal probe storage device has a plurality of probes that may contemporaneously write to, and contemporaneously read from, storage locations of a polymer substrate.
FIG. 1 is a graph 50 showing an exemplary temperature signal 52 of the thermal probe storage device. More specifically, the graph 50 of temperature signal 52 represents the temperature of a distal tip during a read process of memory storage locations located on a polymer substrate. Signal 52 includes random noise, and is typical of a signal resulting from the distal tip moving across the polymer substrate at a speed S1. An ideal signal 54 is shown for reference.
A time period 60, between lines 56 and 58, represents a deflection in temperature signal 52 caused by increased heat energy transfer when the distal tip is within a pit in the polymer substrate that represents a bit of data (e.g., a pit may represent a ‘1’ value and no pit may represent a ‘0’ value). Two exemplary threshold levels 62 and 64 indicate detection levels (including hysteresis) that may be used to determine if the distal tip is reading a ‘1’ value (e.g., the distal tip is within a pit), or if the distal tip is reading a ‘0’ value (e.g., the distal tip is not within a pit).
FIG. 2 is a graph 70 illustrating an exemplary temperature signal 72, representing the temperature of the distal tip passing across memory storage locations of the polymer substrate at an increased speed S2. An ideal signal 74 is shown for reference. Signal 72 includes random noise and is typical of a signal resulting from the distal tip moving across the polymer substrate at speed S2. A time period 80, between lines 76 and 78, represents a deflection in temperature signal 72 caused by increased heat transfer from the distal tip to the polymer substrate when the distal tip is within a pit.
As the distal tip travels across the polymer substrate at the increased speed S2, an amount of time (indicated by period 80 between lines 76 and 78) that the distal tip remains within a pit is reduced, as compared to period 60, FIG. 1. The amount of heat loss to the polymer substrate while the distal tip is within the pit is reduced, and hence the change in temperature of the distal tip is also reduced.
Two exemplary threshold levels 82 and 84 indicate detection levels that may be used to determine if the distal tip is within a pit. As seen in graph 70, the deflection in temperature signal 72 is reduced to a level that is less than the noise level on temperature signal 72. In other words, the signal to noise ratio (SNR) of temperature signal 72 is insufficient to allow consistent detection of data during reading of memory storage locations of the polymer substrate at the increased speed S2.
As appreciated, there is a maximum read speed (e.g., speed S1) at which the thermal probe storage device will correctly operate. This maximum read speed is significantly slower than bit read rates for current hard disk drives. However, data transfer read (and write) rates for the probe storage device are increased due to the parallelism of design. In one example, a probe storage device includes 1024 probes and thereby each bit read operation (e.g., period 60, FIG. 1) returns 1024 bits of information. In comparison, a hard disk drive may, for example, have 16 read heads and therefore return 16 bits of information per hard disk drive read period.
To improve performance of probe storage devices it is desirable to increase read speeds. Hence, there is a need for a probe storage device that overcomes one or more of the drawbacks identified above.